1. Field of the Invention
The present invention relates to a control system and method for a hybrid construction machine. More particularly, the present invention relates to a control system and method for a hybrid construction machine, which can optimize fuel efficiency of a hybrid construction machine system composed of a motor-generator and a typical fuel engine.
2. Description of the Prior Art
In general, a construction machine such as an excavator in the related art has a hydraulic driving system which drives a hydraulic pump by a fuel engine and drives an actuator by hydraulic pressure. The construction machine such as an excavator in the related art performs not only a work that requires the maximum output but also a work that requires an output lower than the maximum output, for example, about 80% or 50% of the maximum output. In the case of performing the work with such a low output, the engine efficiency and the fuel efficiency deteriorate.
FIG. 1 is a necessary torque output relationship diagram of an excavator system in the related art. As illustrated in FIG. 1, in a hydraulic excavator in the related art, an opening area of a main control valve (MCV) 7 is adjusted in accordance with an output of a pilot valve 6 through a user's manipulation of a lever 5. Hydraulic fluid discharged from a hydraulic pump 13 is transferred to respective hydraulic systems with its flow rate adjusted in accordance with the opening area of the MCV 7. Since the driving of the hydraulic pump 13 is performed by a fuel engine 10, the efficiency thereof is relatively low.
FIG. 4 is a view illustrating an engine fuel efficiency map of a hydraulic excavator in the related art. Referring to FIG. 4, a typical engine system in the related art is designed so that the efficiency of a region which has the highest frequency in use is optimized. Accordingly, in a low-output region 22 or a high-output region 20 which has a low frequency in use, the efficiency becomes lowered.
In the construction machine such as the hydraulic excavator in the related art, it is sometimes required to perform working as greatly changing an engine output so as to cope with great load change, and it is required to seek improvement of the engine fuel efficiency by effectively utilizing the engine output. Accordingly, a hybrid technology using an electric motor-generator that is adopted in a hybrid vehicle has been planned to be applied to an excavator. That is, a hybrid construction machine, such as a hybrid excavator, in which an engine is connected to an electric motor-generator, has been proposed. According to the hybrid construction machine, in the case of performing a light-load operation, the motor-generator is operated to generate power to charge a battery using a portion of the engine output, while in the case of performing a heavy-load operation, electric energy is provided from the battery to supplement the engine.
However, the construction machine such as the excavator has the characteristics of an engine output, a torque/speed operation region, and a power transfer device which are quite different from those of a hybrid vehicle, and thus it is not easy to apply the hybrid technology to the construction machine. According to a hybrid construction machine control system proposed in the related art, in which the motor-generator generates power to charge a battery using surplus engine output torque in the case of performing the light-load operation, while in the case of performing the heavy-load operation, electric energy charged in the battery is supplied to the motor-generator to operate the motor-generator as a motor, so that the engine is supplemented as much as the shortage of the engine output torque, it is difficult to seek improvement of the fuel efficiency by effectively utilizing the output of the engine of the construction machine such as the excavator which has the characteristics of working region of diverse loads, engine output, torque/speed operation region, and power transfer device which are quite different from those of the hybrid vehicle. In particular, since the excavator performs various kinds of works, of which working loads are different from one another, such as excavating, dipping-out, leveling, pounding, and the like, the transmission technology for the hybrid vehicle is not adopted in the hybrid excavator in the related art, and thus it is very difficult to optimize the fuel efficiency.
Further, in the construction machine such as the excavator, if the relationship between the kind (or mode) of the work and the engine output or the battery charging state is not considered, problems, such as energy waste, deterioration of working efficiency, and the like, may occur.